An Improved Methodology for Dispersion Compensation and Design of Dense WDM System in Optical Fiber Communication Networks

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1 An Improved Methodology for Dispersion Compensation and Design of Dense WDM System in Optical Fiber Communication Networks Chandra shekhar Prasad Vind 1, Dr. Neelam Srivastava 2 1,2 Department of electronics, Institute of engineering & Technology Lucknow, (U.P.) India Abstract-- In telecommunication, a method for managing dispersion that combines two or more types of single mode fiber to produce the desired dispersion over the entire link span has been proposed. The total dispersion can be set at virtually any value as the contributions from different components may have opposite signs (i.e. either positive or negative) and hence they can partially, or completely, cancel each other. Dispersion-compensating fibers can be either placed at one location or distributed along the length of the fiber link. Typically, dispersion management must consider single-mode fiber chromatic and Polarisation mode dispersion (PMD) dispersion over a range of wavelengths. We design the dense WDM system signals at central wavelengths in the region of 1550 nm. This method offers almost negligible dispersion by reducing the jitter portion in Eye diagram. This method also offers high value of Q-factor and reduced BER in long haul optical communication networks. Keywords--Chromatic dispersion, PMD, DCF, Q-factor, BER, Threshold value, Dense WDM. I. INTRODUCTION WDM Networks offers everlasting demand for bidirectional Information transmission. These systems are Immune to Interference and offers very large Bandwidth, Flexibility and very high level of reliability. However some parameters like Attenuation, Dispersion, Coupling and bending losses degrades its performance. Attenuation can be reduced up to zero level by processing the signal through power amplifiers as well as coupling and bending losses can also be minimized by careful system design. The enormous bandwidth of optical fiber provide a potential to transmit signal at very high speed, yet this bandwidth cannot be fully utilized a significant reason is the fiber dispersion. Usually the fiber dispersion includes intermodal dispersion and polarization mode dispersion. Dispersion is not a significant problem. PMD is the main limitation that confines the optical fiber transmission from utilizing the bandwidth efficiency. However dispersion is the main parameter which needs to be compensated for faithful signal transmission Fiber Bragg s Grating is one of the solution to compensate it, but only up to a certain level. An EDFA can regenerate weak signal but it makes the dispersion worse. Since the dispersion effect accumulate over the multiple amplifier stages therefore the current task of optical fiber communication system design is to solve the fiber dispersion problem specially PMD. There are many technique demonstrated for PMD compensation in both the optical domain and electrical domain. Early strategies to reduce the PMD were focused on reducing the intrinsic PMD of fiber by altering manufacturing process. This leads to low and stable values of PMD in the new generation of single mode fiber being manufactured. The complex impulse baseband impulse response is the backbone to construct the simulation of optical fiber channel. Gaussian noise signals are also added to represent the thermal noise in the channel at the front end of receiver. An Improved methodology for Dispersion Compensation and Dense WDM system design is discussed in this work, which offers much better performance in long haul Optical Fiber Networks. Figure 1: Dispersion management map for two different singlemode fiber types and lengths 370

2 Figure 2: An illustration of DCF for three different wavelength channels II. SIMULATION SETUP The Simulation model of transmitter and Receiver for optical fiber Communication is implemented on OPTISYSTEM-7.0 software using 100 KM long Single mode fiber. Bit rate 2.5 Gaps. NRZ pulse generator has maximum amplitude of 1 auk. Both rise and fall time is 0.05 bit. A CW laser is taken as an optical source having frequency value of THz with sweep power level 13 dbm. MZM have the Excitation ratio 30 db and symmetry factor -1. The loop control system has 2 loops. The PIN photo detector have the Responsitivity 1 A/W and Dark current 10 and the down sampling rate is 800 GHz for the central frequency THz considering thermal noise 2.048e-023 W/Hz. The Random seed index is 11 with the filter sample rate 5 GHz. A fourth order low pass Bessel filter is connected at the output having 100 db depth and sweep value of Cut frequency 0.7 Bit rate Hz. An EDFA is considered having Gain and Noise figure of 20 db, 4 db respectively with power and saturation power level of 10 dbm, the noise BW is 13 THz and noise bin spacing is 125 GHz. For centre frequency of THz. SMF have the reference wavelength of 1550 nm with attenuation 0.25 db/km, Dispersion 16 ps/nm/km and dispersion slope 0.08 ps/nm 2 /km with β 2 =- 20 ps 2 /km and β 3 =0 ps 2 /km. Differential group delay for PMD is taken 3ps/km with the PMD coefficient of 0.5 ps/km. A dispersion compensated fiber is used before the SMF. The total length of fiber channel is remains same, however it segmented in the ration of 1:5 i.e. 17 km DCF and 83 km SMF. The value of dispersion coefficient β 2 for DCF fiber, is calculated here in terms of β 1 (dispersion coefficient for SMF) in such way so that after certain distance the total chromatic dispersion D T must be equal to zero. The parameters for DCF are reference wavelength 1550 nm attenuation 0.6 db/km, dispersion - 80 ps/nm/km, dispersion slope ps/nm 2 /km, β 2 = -20 ps 2 /km, Differential group delay 3 ps/km, PMD coefficient 0.5 ps/km, mean scatter section 50 m, scattering section dispersion 100, lower calculation limit 1200 nm, upper calculation limit 1700 nm, effective area 30 um 2, n 2 = 3e-020 m 2 /w, Raman self-shift time 1 = 14.2 fes, Raman self-shit time 2 = 3 fes,. Raman contribution 0.18 and orthogonal Raman factor In this model we design dense wavelength division multiplexing (DWDM) having channel spacing 0.5nm and 8-channels. In this model MUX and DEMUX have bandwidth 10GHZ, depth 100dB and a second order Bessel filter. In dense WDM system channel spacing should be 100GHZ to 12.5 GHZ (0.1nm to 0.8nm at 1550nm) and number of channel can be increased up to any extent by using minimum channel spacing. 371

3 Figure 3: Simulation Model for 8- channel Dispersion Compensation Technique (DCF) III. RESULT AND DISCUSSION Spectrum analysis Bandwidth of an optical fiber determines the data rate. The mechanism that limits a fiber s bandwidth is known as dispersion. Dispersion is the spreading of the optical pulses as they travel down the fiber. Optical spectrum analyzers (OSA) can divide a light-wave signal into its constituent wavelengths. This means that it is possible to see the spectral profile of the signal over a certain wavelength range. The profile is graphically displayed, with wavelength on the Vertical axis and power on the Horizontal axis. In this way, the many signals combined on a single fiber in a dense wavelength division multiplexing (DWDM) system can be taken apart to perform per-channel analysis of the optical signal and its spectral interaction with the other wavelengths. (a)transmitted spectrum 372

4 (b) (b) Received spectrum Figure 4: Power Vs wavelength The transmitted and Received spectrums are shown in fig.(4) for DCF system which shows that spectrum does not decreases due to other nonlinear effects thus, DCF method offers better frequency spectrum for wavelength routed channels. Eye diagram analysis The eye diagram is also a common indicator of performance in digital transmission systems. The eye diagram is an oscilloscope display of a digital signal, repetitively sampled to get a good representation of its behaviour. In a radio system, the point of measurement may be prior to the modulator in a transmitter, or following the demodulator in a receiver, depending on which portion of the system requires examination. Eye diagram analysis for fourth channel (c) (d) Figure 5: Eye diagram analysis with reference to (a) Q-factor (b) Min BER (c) Threshold value (d) BER Pattern (a) 373

5 Eye diagram analysis for fifth channel (d) (a) Figure 6: Eye diagram analysis with reference to (a) Q-factor (b) Min BER (c) Threshold value (d) BER Patter Eye diagram analysis for eighth channel (b) (a) (c) (b) 374

6 (c) (d) Figure 7: Eye diagram analysis with reference to (a) Q-factor (b) Min BER (c) Threshold value (d) BER Pattern IV. COMPARISON TABLE Parameters Previous Proposed Model Model No. Of Channel 1 8 Q-Factor Channel 1 = 6.46 Channel 2 = Channel 3 = Channel 4 = Channel 5 = Channel 6 = Channel 7 = Channel 8 = Min. BER 0 Channel1= Channel2= Channel3 = Channel 4 = 0 Channel 5 = 0 Channel 6 = 0 Channel 7 = 0 Channel 8 = 0 Power (dbm) Distance (Km) Dispersion Present Negligible Channel Spacing(nm) V. CONCLUSION In this work, an improved methodology The DCF Technique for dispersion compensation in long haul network is discussed. This method offers improved value of performance parameters such as Q-FACTOR, MIN BER and THRESHOLD value. During the analysis of simulation result it is also observed that BER pattern is much better than previous model. Eye diagram shows better value of THRESHOLD and HIGHT which alternatively results in reduced jitter. REFERENCES [1] Alam S. M. Jahangir, Alam M. Rabiul, Hu Guoqing, and Mehrab Md. Zakirul (2011), Bit Error Rate Optimization in Fiber Optic ommunications International Journal of Machine Learning and Computing, Vol. 1, No. 5,PP [2] Manohari R.Gowri and Sabapathi T. (2011), Analysis and Reduction of Polarization Mode Dispersion in an Optical Fiber International Conference on Recent Advancements in Electrical, Electronics and Control Engineering, IEEE proceeding chapter ISBN , pp [3] Pelusi Mark D. (2013), WDM Signal All-Optical Pre compensation of Kerr Nonlinearity in Dispersion-Managed Fibbers IEEE Photonics Technology Letters, Vol. 25, No. 1, pp [4] Guifang Li, Eduardo Mateo and Likai Zhu (2011), Compensation of Nonlinear Effects Using Digital Coherent Receivers OSA/OFC/NFOEC, PP 1-2. [5] Xin Chunsheng, Cao Xiaojun (2008), An Agile Light path Provisioning Paradigm for IP over WDM Optical Networks IEEE proceeding OFC/NFOEC2008. [6] Yan L.S. et al (2005), Performance optimization of RZ data format in WDM systems using tenable pulse width management at the transmitter, J. Lightwave Technol., 23(3), pp [7] Yang Q. et al (2009), Real-time coherent optical OFDM receiver at 2.5GS/s for receiving a 54 Gb/s multi-band signal, OFC 2009 Paper PDPC5. [8] Yao S. et al (2000), Advances in photonic packet switching: An overview, IEEE Communication. Mag., vol. 38, pp [9] Xiang Liu, Douglas M. Gill, and Seth madhavan Chandrasekhar (2006), Optical Technologies and Techniques for High Bit Rate Fiber Transmission Bell Labs Technical Journal 11(2), [10] Xie Chongjin (2013), Chromatic Dispersion Estimation for Single-Carrier Coherent Optical Communications IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 25, NO. 10, pp